Update css-fonts-4/Overview.bs

xiaochengh · web-flow · commit 522b50f56d7a · 2020-09-17T11:06:24.000-07:00
diff --git a/css-fonts-4/Overview.bs b/css-fonts-4/Overview.bs
@@ -2946,7 +2946,7 @@ and sTypoLineGap from the font's OS/2 table, while on Mac, it uses those in the
 available.
 
 When the descriptor value is a percentage, the corresponding metric value is resolved as the
-given percentage multiplied by the used font size. Negative values are illegal.
+given percentage multiplied by the used font size. Negative values are invalid at parse time.
 
 <div class="example">
 	We may override the metrics of Arial as follows:
